In a transistor, the emitter , base and collector are respectively

Options

A. heavily doped , lightly doped , moderately doped
B. heavily doped , moderately doped , lightly doped
C. lightly doped , moderately doped, heavily doped
D. none

Answer

To solve the question regarding the doping levels of the emitter, base, and collector in a transistor, we can break it down step by step:

### Step-by-Step Solution:

1. **Understanding the Structure of a Transistor**:
- A transistor consists of three regions: the emitter, base, and collector. In the case of an NPN transistor, the emitter and collector are n-type materials, while the base is a p-type material.

2. **Doping Levels**:
- **Emitter**: The emitter is heavily doped. This is essential because it needs to inject a large number of charge carriers (electrons in the case of an NPN transistor) into the base region to ensure efficient operation. The heavy doping allows for a high concentration of electrons to flow from the emitter to the base.
- **Base**: The base is lightly doped and very thin. This is crucial because a lightly doped base ensures that only a small amount of current flows through it (IB), which is necessary for the transistor to function effectively. The thinness of the base allows most of the electrons from the emitter to pass through to the collector.
- **Collector**: The collector is moderately doped. This is important because if the collector were heavily doped, it would repel the incoming electrons from the base, reducing the efficiency of the transistor. Moderate doping allows the collector to collect the majority of charge carriers without repelling them.

3. **Conclusion**:
- Therefore, in an NPN transistor:
- The emitter is **heavily doped**.
- The base is **lightly doped**.
- The collector is **moderately doped**.

### Final Answer:
In a transistor, the emitter, base, and collector are respectively: **heavily doped, lightly doped, moderately doped**.

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